Automatic lubrication systems are used on many types of machinery, from large fixed plant to smaller mobile construction and mining equipment. In general they replace previous procedures requiring manual application using grease guns and the like. There is a wide range of equipment available in the market, performing a useful service in improving machine reliability, reducing the hazards of manual access to the machine, reducing the time requirement for maintenance and minimising the quantity of lubricant required.
A typical automatic lubrication system includes a pumping system that receives grease from a reservoir and periodically delivers the grease through supply lines to a number of injectors, which, in turn, deliver prescribed amounts of grease through a feed line to each lubrication point. In the interests of clarity, the conduit between the pump and the injector, usually constructed from a combination of elements including pipes, tubes, hoses and drillings, is called the “supply line”, and similarly, the conduit between the injector and the bearing is called the “feed line”. The generic term “supply conduit” used in the claims of this specification is synonymous with “supply line” as defined above, and similarly the generic term “feed conduit” is synonymous with “feed line”.
The number of injectors varies with the requirement of the equipment, as they are individually connected to a bearing or other mechanism requiring lubrication. This permits the variable requirements of each point to be satisfied.
The injectors incorporate means for individually adjusting the amount of grease dispensed with each shot, and typically provide a visual means of inspecting that they are functioning. For this reason they are usually mounted in a position convenient for maintenance and inspection. On the other hand, the feed line from the injector has to be routed to its appropriate bearing, which will sometimes be situated in normally inaccessible parts of the machine.
There are many types of pumping systems, powered by electric motors, compressed air, hydraulic pressure from the machine's hydraulic system, or even manually. The frequency of operation is often controlled by an electrical timer, or computer performing the same function, or can be linked to the operation duty of the machine. Typically, each operation consists of pumping grease from a reservoir to a fixed pressure, holding the pressure for at least long enough for the pressure to reach all the injectors against the viscous drag of the grease in the supply lines, and then venting this pressure back to the grease reservoir to allow the injectors to reset.
There are three main types of injector systems in common use. The simplest of these is the single line system, where the pump periodically pressurises the injectors, causing them to inject their adjusted amount of grease down the feed line to the bearing, then vents the pressure so that the injectors can reset ready for the next shot. This system can have disadvantage with longer supply lines between the pump and injectors in that the viscosity of the grease can lead to slow venting times so that the maximum frequency of grease application has to be reduced to ensure that the injectors reset. Injector designs that have a higher reset pressure are then superior in these conditions.
A second type is the dual line system, which overcomes the reset time problem by running two lines to each injector and reversing the pressure between the lines. The injectors are then designed to have a bidirectional capability so that each reversal of pressure causes the injector to discharge its prescribed amount of grease to a feed line. The full pump pressure is then used to overcome the effects of grease viscosity.
The third type is the progressive system, where banks of injectors automatically cycle as long as pressure is applied, and do not require any form of resetting. Lower cost versions of this system do not provide individual adjustment of each output. They are sensitive to particulate contamination, and a stoppage of one output also causes all the others in the same bank to stop as well.
In summary, the single line system offers many advantages over other systems, but needs a high reset pressure to be usable with long supply lines.
Operation of a lubrication system is only useful when it is functioning correctly. If it is the case that the operator can use the machine and continue to operate unknowingly with a faulty system then there is the possibility that the automatic system is less certain than using a manual grease gun for each point. It would then be an important improvement if the system verifies that grease is reaching the bearing and alerts the operator if there is a problem.
The most vulnerable part of the system in many machines is the feed line from the injector to the bearing, as this is often not easily accessible, adjacent to moving parts, and subject to misadventure, such as rocks falling out of a loader bucket. There are some systems that apply sensors to the lubrication point using wires within the feed lines connecting back to a monitoring computer, but these are expensive and complex, and the majority of installations trust to luck and frequent inspections, and accept the occasional bearing failure caused by a lubrication system shortcoming as a reality of operation.
In the interests of brevity, this application refers to the lubricant as grease, being the most common substance, but other lubricants, such as oil, and synthetic liquids, or gels, can be used with the invention. Similarly, where components such as pistons are referred to as having a diameter, it will be obvious that in at least some cases the same functionality can be achieved with other cross-sections such as oval or square. Similarly again for brevity, the lubrication system is described as delivering lubricant to bearings, with this being used as a generic term to describe any structure receiving an injected fluid at one or more lubrication points.
It should also be recognised that although the invention has been devised for the lubrication of bearings, in its broadest aspects it could be used for the precise and reliable delivery of predetermined qualities of any liquid to an end point. Such applications might include, although not be limited to; dispensing of disinfectants or anti-bacterial agents into cooling towers; medical applications; or automatic adhesive applications. The description of the delivery of lubricant to bearings throughout this specification should be regarded as a specific example of delivery of a generic liquid to any end point.
Using common fluid power terminology throughout this specification; a check valve is a one-way valve that permits free flow in one direction, but is closed to flow in the reverse direction; a “pressurising valve” allows flow at least in one direction while imposing a set pressure rise substantially independent of the flow rate, often, but not always, also acting to prevent flow in the reverse direction; a “relief valve” is a pressurising valve that is sensitive to the downstream pressure so that the upstream pressure is the sum of the set pressure and the downstream pressure; and, a “sequence valve” is not sensitive to downstream pressure so that the upstream pressure is constant regardless of the downstream pressure, at least until downstream pressure exceeds the pressure setting of the valve.